1. Field of the Invention
This invention relates generally to threaded fasteners and the like, and more particularly to friction gripping fastener apparatus which resists releasing when subjected to vibration.
2. Description of the Prior Art
Moving machinery inherently creates vibrations which tend to loosen fasteners, particularly screw threaded fasteners, employed to hold together various parts of the machinery. Accordingly, various kinds of locking fasteners are used to prevent loosening of the fasteners in service. Typical of these locking fasteners are those employing a wedge principle, examples of which can be found in U.S. Pat. Nos. 646,898, issued Apr. 3, 1900, to H. A. Deiters; 788,324, issued Apr. 25, 1905, to W. L. Morrow; U.S. Pat. No. 1,290,357, issued Jan. 7, 1919, to G. W. Rissler; U.S. Pat. No. 2,886,085, issued May 12, 1959, to A. W. Morton; and U.S. Pat. No. 4,378,187, issued Mar. 29, 1983, to R. L. Fullerton. Most of these known locking arrangements have the disadvantage of requiring a nut assembly which is substantially double the height of a single nut. This problem is of particular concern when dealing with certain kinds of motor vehicles, such as racing cars, and with aircraft, particularly helicopters, where vibration and load problems are particularly severe, yet there is little space available to accommodate fasteners. The aforementioned U.S. Pat. No. 4,378,187 overcomes this problem by providing a nut assembly in which a jam nut portion is arrangeable within a cavity provided in a nut casing. This known assembly, however, is rather complex inasmuch as it has several parts and numerous sloping surfaces which must be made to rather close tolerances.
Another class of locking fasteners which is well known and widely used employs a deformable element to achieve locking. Examples of such locking arrangements can be found in U.S. Pat. Nos. 1,720,799, issued July 16, 1929, to M. P. McLaughlin, and U.S. Pat. No. 2,429,103, issued Oct. 14, 1947, to R. Mitchell.
There is known a class of metals referred to as "memory metals" because they have the ability of recovering to a non-deformed configuration after having been temporarily deformed. An important group of such materials are nickel-base alloys essentially comprising nickel and titanium. These metals possess a thermoelastic transition between a martensitic state and an austenitic state, wherein the metal can be deformed dimensionally while in the martensitic state and recover to its non-deformed dimension or configuration in the austenitic state. The material normally is in the austenitic state at normal or ambient temperatures, and is transformed into the martensitic state by cooling the metal below a temperature inherent to the material.
Examples of nickel-titanium based memory metals can be found in U.S. Pat. Nos. 3,174,851, issued Mar. 23, 1965 to W. J. Buehler et al, and U.S. Pat. No 3,351,463, issued Nov. 7, 1967 to A. G. Rozner et al; while a method for growing single crystals of such metals can be found in U.S. Pat. No. 3,352,722, issued Nov. 14, 1967 to F. E. Wang et al.
Various examples of uses of memory metals as described above can be found in U.S. Pat. Nos. 3,285,470, issued Nov. 15, 1966 to E. H. Frei et al; U.S. Pat. No. 3,391,882, issued July 9, 1968 to J. F. Johnson et al; U.S. Pat. No. 3,403,238, issued Sept. 24, 1968, to W. J. Buehler et al; U.S. Pat. No. 3,416,342, issued Dec. 17, 1968, to D. Goldstein et al; U.S. Pat. No. 4,379,575, issued Apr. 12, 1983, to C. L. Martin; and U.S. Pat. No. 4,930,599, issued June 28, 1983, to H. C. Broyles.
Additional examples of applications of memory metals as described above can be found in the two U.S. patents issued to R. F. Otte et al, U.S. Pat. Nos. 3,740,839 and U.S. Pat. No. 3,861,030, issued June 26, 1973, and Jan. 21, 1975, respectively, and in U.S. Pat. No. 4,022,519, issued May 10, 1977 to F. W. L. Hill.
Also of interest with regard to memory materials, their composition and applications, is British Pat. No. 1,116,158, published June 6, 1968.